Electroluminescent display device

ABSTRACT

An electroluminescent display device includes a thin film transistor disposed on a substrate; a passivation layer disposed on the thin film transistor; a plurality of metallic patterns disposed to be spaced apart from each other on the passivation layer; a reflective electrode disposed conforming to the shapes of the plurality of metallic patterns and a top surface of the passivation layer and including a plurality of protruding portions; an overcoat layer disposed on the passivation layer and the reflective electrode and including an opening configured to expose a top surface of each of the plurality of protruding portions; a first electrode disposed on the reflective electrode and the overcoat layer and electrically connected to the reflective electrode; an light-emitting layer disposed on the first electrode; and a second electrode disposed on the light-emitting layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanPatent Application No. 10-2017-0163172, filed on Nov. 30, 2017, in theKorean Intellectual Property Office, which is incorporated herein byreference in its entirety.

BACKGROUND Technical Field

The present disclosure relates to an electroluminescent display device,and more particularly, to an electroluminescent display device capableof improving light extraction efficiency and widening a viewing angle.

Description of the Related Art

In recent years, flat panel displays having excellent characteristicssuch as being thin, lightweight, and having low power consumption havebeen widely developed and applied to various fields.

Among the flat panel displays, an electroluminescent display device is adevice in which electrical charge carriers are injected into alight-emitting layer formed between a cathode, which is anelectron-injecting electrode, and an anode, which is a hole-injectingelectrode, such that excitons are formed, and then radiativerecombination of the excitons occurs, thereby emitting light.

The electroluminescent display device can be formed using a flexiblesubstrate such as plastic because it is self-luminous, and has excellentcontrast ratios. Further the electroluminescent display device has aresponse time of several micro seconds, and there are advantages indisplaying moving images. The electroluminescent display device also haswide viewing angles and is stable under low temperatures. Since theelectroluminescent display device is driven by a low voltage of directcurrent DC 5V to 15V, it is easy to design and manufacture drivingcircuits.

FIG. 1 is a schematic cross-sectional view of a related artelectroluminescent display device.

As illustrated in FIG. 1, an electroluminescent display device 1includes a substrate 10, a thin film transistor Tr disposed on thesubstrate 10, and a light-emitting diode D disposed on the substrate 10and connected to the thin film transistor Tr. An encapsulation layer(not shown) may be disposed on the light-emitting diode D.

The light-emitting diode D includes a first electrode 41, alight-emitting layer 42, and a second electrode 43, wherein light fromthe light-emitting layer 42 is output to the outside through the secondelectrode 43.

The light emitted from the light-emitting layer 42 passes throughvarious configurations of the electroluminescent display device 1 andoutput toward an upper portion of the electroluminescent display device1.

However, an optical waveguide mode which is configured by a surfaceplasmon component generated at a boundary between a metal and thelight-emitting layer 42 and the light-emitting layer 42 inserted betweenreflective layers at both sides accounts for about 60 to 70% of emittedlight.

Accordingly, among light emitted from the light-emitting layer 42, raysof light that are trapped in the electroluminescent display device 1instead of exiting the electroluminescent display device 1 are present.Thus, there is a problem in that light extraction efficiency of theelectroluminescent display device 1 is degraded.

BRIEF SUMMARY

Accordingly, embodiments of the present disclosure are directed to anelectroluminescent display device that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

It is an object of the present disclosure to provide anelectroluminescent display device that is able to improve lightextraction efficiency and widen a viewing angle.

To achieve the above-described object, the present disclosure providesan electroluminescent display device including a thin film transistordisposed on a substrate; a passivation layer disposed on the thin filmtransistor; a plurality of metallic patterns disposed to be spaced apartfrom each other on the passivation layer; a reflective electrodedisposed conforming to the shapes of the plurality of metallic patternsand a top surface of the passivation layer and including a plurality ofprotruding portions; an overcoat layer disposed on the passivation layerand the reflective electrode and including an opening configured toexpose a top surface of each of the plurality of protruding portions; afirst electrode disposed on the reflective electrode and the overcoatlayer and electrically connected to the reflective electrode; anlight-emitting layer disposed on the first electrode; and a secondelectrode disposed on the light-emitting layer.

In another aspect, an electroluminescent display device includes asubstrate including one or more pixels; and a light-emitting structuredisposed in each of the pixels, wherein the light-emitting structurecomprises a second electrode, a reflective electrode, and alight-emitting layer disposed between the second electrode and thereflective electrode, or comprises a second electrode, a reflectiveelectrode, a light-emitting layer disposed between the second electrodeand the reflective electrode, and a first electrode disposed between thelight-emitting layer and the reflective electrode, wherein each of thepixels comprises a plurality of micro cavity areas disposed to be spacedapart from each other and one or more non-micro cavity area disposedbetween the micro cavity area, a combined thickness in a verticaldirection of the light-emitting structure from the reflective electrodeto the second electrode has a different value in the micro cavity areafrom that in the non-micro cavity area, and the light-emitting structureis configured to produce a micro cavity effect, and wherein each of thesecond electrode and the reflective electrode is formed to be flat inthe micro cavity area and at least one of the second electrode and thereflective electrode is formed to comprise a non-flat surface in thenon-micro cavity area or wherein each of the first electrode, the secondelectrode, and the reflective electrode is formed to be flat in themicro cavity area and at least one of the first electrode, the secondelectrode, and the reflective electrode is formed to comprise a non-flatsurface in the non-micro cavity area.

It is to be understood that both the foregoing general description andthe following detailed description are by example and explanatory, andare intended to provide further explanation of the present disclosure asclaimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present disclosure and which are incorporated inand constitute a part of this specification, illustrate embodiments ofthe present disclosure and together with the description serve toexplain various principles of the present disclosure. In the drawings:

FIG. 1 is a cross-sectional view schematically illustrating a relatedart electroluminescent display device;

FIG. 2 is a circuit diagram illustrating a single subpixel area of anelectroluminescent display device according to an embodiment of thepresent disclosure;

FIG. 3 is a cross-sectional view schematically illustrating theelectroluminescent display device according to an embodiment of thepresent disclosure;

FIG. 4 is an enlarged view of portion A in FIG. 3;

FIG. 5 is a view schematically illustrating an optical path of theelectroluminescent display device according to the embodiment of thepresent disclosure;

FIGS. 6A to 6C are plan views schematically illustrating metallicpatterns of the electroluminescent display device according to theembodiment of the present disclosure;

FIGS. 7A to 7D are views schematically illustrating optical paths inaccordance with a distance between the plurality of metallic patterns ofthe electroluminescent display device according to the embodiment of thepresent disclosure; and

FIGS. 8A to 8C are views schematically illustrating optical paths inaccordance with an angle between a second surface and each of first andsecond inclined surfaces of each metallic pattern of theelectroluminescent display device according to the embodiment of thepresent disclosure.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will bedescribed with reference to the accompanying drawings.

FIG. 2 is a circuit diagram illustrating a single subpixel area of anelectroluminescent display device according to an embodiment of thepresent disclosure.

As illustrated in FIG. 2, the electroluminescent display deviceaccording to the embodiment of the present disclosure includes a gateline GL, a data line DL, a switching thin film transistor Ts, a drivingthin film transistor Td, a storage capacitor Cst and a light-emittingdiode D. The gate line GL and the data line DL cross each other todefine a subpixel area SP. The switching thin film transistor Ts, thedriving thin film transistor Td, the storage capacitor Cst and thelight-emitting diode D are formed in the subpixel area SP.

More specifically, a gate electrode of the switching thin filmtransistor Ts is connected to the gate line GL and a source electrode ofthe switching thin film transistor Ts is connected to the data line DL.A gate electrode of the driving thin film transistor Td is connected toa drain electrode of the switching thin film transistor Ts, and a sourceelectrode of the driving thin film transistor Td is connected to a highvoltage supply VDD. An anode of the light-emitting diode D is connectedto a drain electrode of the driving thin film transistor Td, and acathode of the light-emitting diode D is connected to a low voltagesupply VSS. The storage capacitor Cst is connected to the gate electrodeand the drain electrode of the driving thin film transistor Td.

The electroluminescent display device is driven to display an image. Forexample, when the switching thin film transistor Ts is turned on by agate signal applied through the gate line GL, a data signal from thedata line DL is applied to the gate electrode of the driving thin filmtransistor Td and an electrode of the storage capacitor Cst through theswitching thin film transistor Ts.

When the driving thin film transistor Td is turned on by the datasignal, an electric current flowing through the light-emitting diode Dis controlled, thereby displaying an image. The light-emitting diode Demits light due to the current supplied through the driving thin filmtransistor Td from the high voltage supply VDD.

That is, the amount of the current flowing through the light-emittingdiode D is proportional to the magnitude of the data signal, and theintensity of light emitted by the light-emitting diode D is proportionalto the amount of the current flowing through the light-emitting diode D.Thus, subpixel areas SP show different gray levels depending on themagnitude of the data signal, and as a result, the electroluminescentdisplay device displays an image.

The storage capacitor Cst maintains charges corresponding to the datasignal for a frame when the switching thin film transistor Ts is turnedoff. Accordingly, even if the switching thin film transistor Ts isturned off, the storage capacitor Cst allows the amount of the currentflowing through the light-emitting diode D to be constant and the graylevel shown by the light-emitting diode D to be maintained until a nextframe.

A transistor and/or a capacitor other than the switching and drivingthin film transistors Ts and Td and the storage capacitor Cst may befurther added in the subpixel area SP.

FIG. 3 is a cross-sectional view schematically illustrating theelectroluminescent display device according to an embodiment of thepresent disclosure.

As illustrated in FIG. 3, an electroluminescent display device 100according to the embodiment of the present disclosure may include afirst substrate 110, a thin film transistor 120, a plurality of metallicpatterns MP, a reflective electrode RE, an overcoat layer 160, and alight-emitting diode D.

The electroluminescent display device 100 according to the embodiment ofthe present disclosure is illustrated as being a top emission type inwhich light from a light-emitting layer 142 is output to the outsidethrough a second electrode 143, but embodiments are not limited thereto.

The electroluminescent display device 100 according to the embodiment ofthe present disclosure may include a thin film transistor 120 whichincludes a gate electrode 121, an active layer 122, a source electrode123, and a drain electrode 124 on the first substrate 110.

Specifically, the gate electrode 121 of the thin film transistor 120 anda gate insulation layer 131 may be disposed on the first substrate 110.

The active layer 122, which overlaps the gate electrode 121, may bedisposed on the gate insulation layer 131.

An etch stopper 132 for protecting a channel region of the active layer122 may be disposed on the active layer 122.

The source electrode 123 and the drain electrode 124 may be disposed onthe active layer 122 and contact the active layer 122.

The electroluminescent display device to which the embodiment of thepresent disclosure is applicable is not limited to that illustrated inFIG. 3. The electroluminescent display device may further include abuffer layer disposed between the first substrate 110 and the activelayer 122, and the etch stopper 132 may not be disposed thereon.

For convenience of description, only the driving thin film transistorhas been illustrated from among various thin film transistors that maybe included in the electroluminescent display device 100. Although thethin film transistor 120 will be described as having an invertedstaggered structure or bottom gate structure in which the gate electrode121 is disposed at an opposite side of the source electrode 123 and thedrain electrode 124 with respect to the active layer 122, this is merelyan example, and a thin film transistor having a coplanar structure ortop gate structure in which the gate electrode 121 is disposed at thesame side as the source electrode 123 and the drain electrode 124 withrespect to the active layer 122 may also be used.

A passivation layer 133 may be disposed on the drain electrode 124 andthe source electrode 123.

In this case, although the passivation layer 133 is illustrated asflattening an upper portion of the thin film transistor 120, thepassivation layer 133 may also be disposed along the shapes of surfacesof elements located below the passivation layer 133 instead offlattening the upper portion of the thin film transistor 120.

A plurality of metallic patterns MP which are spaced apart from eachother may be disposed on the passivation layer 133 in an emissive areaEA of the electroluminescent display device 100 according to theembodiment of the present disclosure.

That is, the plurality of metallic patterns MP spaced apart from eachother may be disposed in the emissive area EA, and the passivation layer133 may be exposed between adjacent metallic patterns MP.

In this case, emissive area EA refers to an area in which thelight-emitting layer 142 emits light by the first electrode 141 and thesecond electrode 143.

Each of the plurality of metallic patterns MP may be formed of a singlelayer or multiple layers formed of copper (Cu), molybdenum (Mo),titanium (Ti), or an alloy thereof, but embodiments are not limitedthereto.

The plurality of metallic patterns MP may have a trapezoidalcross-section, but embodiments are not limited thereto.

In the electroluminescent display device 100 according to the embodimentof the present disclosure, the reflective electrode RE may be disposedconforming to the shapes of the plurality of metallic patterns MP and atop surface of the passivation layer 133.

That is, the reflective electrode RE may include a plurality ofprotruding portions PP formed conforming to the shapes of the pluralityof metallic patterns MP.

A top surface of each of the plurality of protruding portions PP may beformed to be flat.

The reflective electrode RE may be formed of an APC alloy, butembodiments are not limited thereto.

The APC alloy refers to an alloy of silver (Ag), palladium (Pd), andcopper (Cu).

The reflective electrode RE may be connected to the source electrode 123of the thin film transistor 120 through a contact hole formed in thepassivation layer 133. However, embodiments are not limited thereto, andthe first electrode 141 on the reflective electrode RE may be connectedto the source electrode 123 of the thin film transistor 120.

The electroluminescent display device 100 according to the embodiment ofthe present disclosure has been described as an example in which thethin film transistor 120 is an N-type thin film transistor and thereflective electrode RE is connected to the source electrode 123, butembodiments are not limited thereto. When the thin film transistor 120is a P-type thin film transistor, the reflective electrode RE may alsobe connected to the drain electrode 124.

The reflective electrode RE may be separately formed in each pixel area.

The shapes of the plurality of metallic patterns MP and the reflectiveelectrode RE will be described in more detail below.

The overcoat layer 160 may be disposed on the passivation layer 133 andthe reflective electrode RE.

The overcoat layer 160 of the electroluminescent display device 100according to the embodiment of the present disclosure may include aplurality of openings 160 a.

The plurality of openings 160 a may be formed to correspond to theplurality of protruding portions PP of the reflective electrode RE,respectively.

That is, the overcoat layer 160 may be formed on the reflectiveelectrode RE corresponding to an area between adjacent metallic patternsMP, and the top surface of each of the plurality of protruding portionsPP of the reflective electrode RE may be disposed at the opening 160 aof the overcoat layer 160 and contact the first electrode 141.

Accordingly, the top surface of the reflective electrode RE which areexposed through the opening 160 a and the top surface of the overcoatlayer 160 may be formed to be flat without a stepped part. Namely, theexposed top surface of the reflective electrode RE may be flush with thetop surface of the overcoat layer 160.

The overcoat layer 160 including the openings 160 a, each of which isconfigured to expose the top surface of each of the plurality ofprotruding portions PP of the reflective electrode RE, may be formedthrough a process such as photolithography, wet etching, and dryetching.

The overcoat layer 160 may be formed of an organic material having arefractive index of about 1.5 to 1.55, but embodiments are not limitedthereto.

The first electrode 141 may be disposed on the overcoat layer 160 andthe reflective electrode RE which is exposed through the openings 160 a.

The first electrode 141 disposed on the overcoat layer 160 and thereflective electrode RE which is exposed through the openings 160 a maybe formed to be flat and be separately formed in each subpixel area.However, embodiments are not limited thereto.

In this case, the first electrode 141 may be an anode or cathode forsupplying one of electrons or holes to the light-emitting layer 142.

A case in which the first electrode 141 of the electroluminescentdisplay device according to the embodiment of the present disclosure isan anode will be described as an example.

The first electrode 141 may include any one selected from the groupconsisting of indium tin oxide (ITO), indium zinc oxide (IZO), zinc tinoxide (ZTO), tin oxide (SnO2), zinc oxide (ZnO), indium oxide (In2O3),gallium indium tin oxide (GITO), indium gallium zinc oxide (IGZO), zincindium tin oxide (ZITO), indium gallium oxide (IGO), gallium oxide(Ga2O3), aluminum zinc oxide (AZO), and gallium zinc oxide (GZO).

The first electrode 141 may contact the top surfaces of the plurality ofprotruding portions PP of the reflective electrode RE.

Accordingly, a micro cavity effect may be obtained in an area in whichthe first electrode 141 contacts the plurality of protruding portions PPof the reflective electrode RE.

The first electrode 141 may also be electrically connected to thelight-emitting layer 142 by contacting the light-emitting layer 142 witha conductive material therebetween.

The first electrode 141 may have a refractive index of about 1.8 orhigher, but embodiments are not limited thereto.

A bank layer 136 may be disposed on the overcoat layer 160 and the firstelectrode 141.

The bank layer 136 may include an open portion 136 a exposing the firstelectrode 141.

The bank layer 136 may be disposed between adjacent pixel (or subpixel)areas and serve to differentiate the adjacent pixel (or subpixel) areas.

The bank layer 136 may be formed of a photo acrylic organic materialhaving a refractive index of 1.6 or lower, but embodiments are notlimited thereto.

The light-emitting layer 142 may be disposed on the first electrode 141and the bank layer 136.

The light-emitting layer 142 may have a tandem white structure in whicha plurality of light-emitting layers are stacked to emit white light.

For example, the light-emitting layer 142 may include a firstlight-emitting layer configured to emit blue light and a secondlight-emitting layer disposed on the first light-emitting layer andconfigured to emit light having a color which turns white when mixedwith blue.

The second light-emitting layer may be a light-emitting layer configuredto emit yellow-green light.

The light-emitting layer 142 may include only a light-emitting layerthat emits one of blue light, red light, and green light.

The light-emitting layer 142 may be disposed in a shape which followsthe morphology of the first electrode 141 in the emissive area EA.

That is, the light-emitting layer 142 may be formed to be flat in theemissive area EA.

The light-emitting layer 142 may be formed of an organic material havinga refractive index of about 1.8 or higher, but embodiments are notlimited thereto. The light-emitting layer 142 may also be formed of aninorganic luminescent material such as a quantum dot.

The second electrode 143 for supplying one of electrons or holes to thelight-emitting layer 142 may be disposed on the light-emitting layer142.

In this case, the second electrode 143 may be an anode or a cathode.

A case in which the second electrode 143 of the electroluminescentdisplay device 100 according to an embodiment of the present disclosureis a cathode will be described as an example.

The second electrode 143 may be formed of a transparent conductivematerial (TCO) such as ITO and IZO or may be formed of asemi-transmissive conductive material such as magnesium (Mg), silver(Ag), or an alloy of Mg and Ag.

The second electrode 143 is disposed in a shape which follows themorphology of the light-emitting layer 142.

That is, the second electrode 143 may be formed to be flat in theemissive area EA.

The first electrode 141, the light-emitting layer 142, and the secondelectrode 143 form the light-emitting diode D.

An encapsulation layer (not shown) may be formed on the second electrode143, and the electroluminescent display device 100 according to theembodiment of the present disclosure may be implemented by attaching asecond substrate (not shown) and the encapsulation layer (not shown) ofthe first electrode 110.

Here, a color filter (not shown) and a black matrix (not shown) may beformed on the second substrate.

FIG. 4 is an enlarged view of portion A in FIG. 3.

As illustrated in FIG. 4, in the electroluminescent display device 100according to the embodiment of the present disclosure, the plurality ofmetallic patterns MP, the reflective electrode RE, the overcoat layer160, the first electrode 141, the light-emitting layer 142, and thesecond electrode 143 may be disposed on the passivation layer 133.

That is, the plurality of metallic patterns MP, which are spaced apartfrom each other, may be disposed on the passivation layer 133 in theemissive area EA.

Here, each of the plurality of metallic patterns MP may include a firstsurface M1 contacting a top surface P1 of the protruding portion PP, asecond surface M2 contacting the passivation layer 133, and first andsecond inclined surfaces M3 and M4 connecting the first surface M1 andthe second surface M2.

Here, the first surface M1 and the second surface M2 may be formed to beflat, and an area of the second surface M2 may be greater than an areaof the first surface M1.

An angle θ formed between the second surface M2 and each of the firstand second inclined surfaces M3 and M4 may be an acute angle.

The acute angle may be in a range of 20° to 70°, but embodiments are notlimited thereto.

That is, each of the plurality of metallic patterns MP may have atrapezoidal cross-section, but embodiments are not limited thereto.

In addition, the plurality of metallic patterns MP may be disposed at adistance G from each other.

Accordingly, the passivation layer 133 may be exposed in an area inwhich the plurality of metallic patterns MP is spaced apart from eachother. Namely, the passivation layer 133 may be exposed in an areabetween adjacent metallic patterns MP.

The distance G at which the plurality of metallic patterns MP are spacedapart from each other may be in a range of 0.5 μm to 2 μm, butembodiments are not limited thereto.

A length d of the first surface M1 of each of the plurality of metallicpatterns MP may be in a range of 1 μm to 5 μm, but embodiments are notlimited thereto.

Further, a height H of each of the plurality of metallic patterns MP maybe in a range of 0.5 μm to 1 μm, but embodiments are not limitedthereto.

The height H of the metallic pattern MP refers to a distance between thefirst surface M1 and the second surface M2.

Each of the plurality of metallic patterns MP may be formed of a singlelayer or multiple layers formed of Cu, M, Ti, or an alloy thereof, butembodiments are not limited thereto.

In the electroluminescent display device 100 according to the embodimentof the present disclosure, the reflective electrode RE may be disposedconforming to the shapes of the plurality of metallic patterns MP andthe top surface of the passivation layer 133.

That is, the reflective electrode RE may include the plurality ofprotruding portions PP and connecting portions CP connecting theplurality of protruding portions PP along the shapes of the plurality ofmetallic patterns MP and the top surface of the passivation layer 133.

Each of the plurality of protruding portions PP may include a topsurface P1 contacting the first electrode 141 and side surfaces P2 andP3 connecting the top surface P1 and the connecting portion CP. Incertain embodiments of the present disclosure, the top surface P1 andside surfaces P2 and P3 of each protruding portions PP may refer to atop surface section P1 and side surface sections P2 and P3,respectively, and may be considered to be interchangeable with eachother, instead of a merely surface.

The side surfaces P2 and P3 may have a predetermined slope.

The connecting portions CP may be disposed between the plurality ofprotruding portions PP and be in contact with the passivation layer 133.

The top surface P1 of each of the plurality of protruding portions PPand the connecting portions CP may be formed to be flat. That is, in thereflective electrode RE, flat top surfaces P1 and flat connectingportions CP, which have different heights, may be alternately disposed.

As described above, in the electroluminescent display device 100 of FIG.3 according to the embodiment of the present disclosure, by disposingthe plurality of metallic patterns MP, which are spaced apart from eachother, on the passivation layer 133 and forming the reflective electrodeRE configured to cover the passivation layer 133 and the plurality ofmetallic patterns MP, the reflective electrode RE may be formed in sucha way that the flat top surfaces P1 of the protruding portions PP andthe flat connecting portions CP, which have different heights, arealternately disposed, and the inclined side surfaces P2 and P3 aredisposed to connect the flat top surfaces P1 of the protruding portionsPP and the flat connecting portions CP.

In addition, the overcoat layer 160 may be disposed on the passivationlayer 133 and the reflective electrode RE.

In this case, the overcoat layer 160 of the electroluminescent displaydevice 100 of FIG. 3 according to the embodiment of the presentdisclosure may include the opening 160 a configured to expose the topsurface P1 of each of the plurality of protruding portions PP of thereflective electrode RE.

That is, by filling spaces between the plurality of protruding portionsPP of the reflective electrode RE with the overcoat layer 160, thereflective electrode RE and the first electrode 141 are electricallyconnected to each other through the opening 160 a of the overcoat layer160 while the overcoat layer 160 flattens upper portions of thepassivation layer 133 and the reflective electrode RE.

The overcoat layer 160 may be formed of an organic material having arefractive index of about 1.5 to 1.55, but embodiments are not limitedthereto.

The first electrode 141 may be disposed on the reflective electrode REand the overcoat layer 160.

The first electrode 141 may be formed of an amorphous metal oxide havinga refractive index of about 1.8 or higher, but embodiments are notlimited thereto.

The first electrode 141 may be disposed to be flat on the reflectiveelectrode RE and the overcoat layer 160.

Therefore, the first electrode 141 may contact the top surfaces P1 ofthe plurality of protruding portions PP of the reflective electrode REand may not contact the side surfaces P2 and P3 and the connectingportions CP of the reflective electrode RE.

Accordingly, a micro cavity phenomenon may occur in an area in which thefirst electrode 141 contacts the top surfaces P1 of the plurality ofprotruding portions PP of the reflective electrode RE.

The micro cavity phenomenon refers to varying an emission spectrumthrough repeated reflection of light by suitably adjusting thicknessesof respective electrodes and the light-emitting layer 142 in thelight-emitting diode D, which includes the reflective electrode RE, thefirst electrode 141 (anode), the light-emitting layer, and the secondelectrode 143 (cathode).

The light-emitting layer 142 may be disposed on the first electrode 141,and the light-emitting layer 142 may be formed to be flat in theemissive area EA of FIG. 3.

The light-emitting layer 142 may be formed of an organic material havinga refractive index of about 1.8 or higher, but embodiments are notlimited thereto. The light-emitting layer 142 may also be formed of aninorganic luminescent material such as a quantum dot.

The second electrode 143 may be disposed on the light-emitting layer142, and the second electrode 143 may be formed to be flat in theemissive area EA of FIG. 3.

As described above, the first electrode 141, the light-emitting layer142, and the second electrode 143 form the light-emitting diode D.

The light-emitting diode D may be formed to be flat in the emissive areaEA.

Through such a structure, in the electroluminescent display device 100of FIG. 3 according to the embodiment of the present disclosure, lightextraction efficiency and color gamut may be improved using the microcavity phenomenon in a micro cavity area MCA in which the firstelectrode 141 contacts the top surfaces P1 of the plurality ofprotruding portions PP of the reflective electrode RE.

In a non-micro cavity area NMCA, which is an area corresponding to theside surfaces P2 and P3 of the plurality of protruding portions PP andthe connecting portions CP of the reflective electrode RE that do notcontact the first electrode 141 and in which the micro cavity phenomenondoes not occur, light, which has been unable to be output to the outsidedue to being totally reflected inside the light-emitting diode D, may bereflected upward so as to be extracted to the outside. In this way,light extraction efficiency may be further improved. Particularly, inthe non-micro cavity area NMCA, since the straightness of light isdecreased due to the shape of the reflective electrode RE and light isoutput in a lateral direction, a phenomenon, in which luminancedecreases and a color shift occurs from a color with a long wavelengthto a color with a short wavelength as a viewing angle increases in therelated art electroluminescent display device to which the micro cavityeffect is applied, may be effectively prevented.

FIG. 5 is a view schematically illustrating an optical path of theelectroluminescent display device according to the embodiment of thepresent disclosure. Description will be given with reference to FIGS. 4and 5.

As illustrated in FIG. 5, the electroluminescent display device 100 ofFIG. 3 according to the embodiment of the present disclosure may includea non-micro cavity area NMCA, which corresponds to the side surfaces P2and P3 and the connecting portions CP of the reflective electrode REthat do not contact the first electrode 141, disposed between a microcavity area MCA and another micro cavity area MCA in which the firstelectrode 141 contacts the top surfaces P1 of the plurality ofprotruding portions PP of the reflective electrode RE.

Light L1 which is output to the outside using the micro cavityphenomenon in the micro cavity area MCA and light L2 which is outputupward by being reflected through the side surfaces P2 and P3 and theconnecting portions CP of the reflective electrode RE in the non-microcavity area NMCA may be mixed so that a viewing angle is widened whilelight extraction efficiency is improved.

That is, since the straightness of light output is decreased due to theshape of the reflective electrode RE and light is output in a lateraldirection in the non-micro cavity area NMCA, the phenomenon, in whichluminance decreases and a color shift occurs from a color with a longwavelength to a color with a short wavelength as a viewing angleincreases in the related art electroluminescent display device to whichthe micro cavity effect is applied, may be effectively prevented.

FIGS. 6A to 6C are plan views schematically illustrating metallicpatterns of the electroluminescent display device according to theembodiment of the present disclosure.

As illustrated in FIGS. 6A to 6C, in the electroluminescent displaydevice 100 of FIG. 3 according to the embodiment of the presentdisclosure, a plurality of metallic patterns MP may be disposed on thepassivation layer 133.

That is, as illustrated in FIG. 6A, each of the plurality of metallicpatterns MP may have a quadrilateral shape in plan view, each of theplurality of metallic patterns MP may be disposed to be spaced apartfrom each other, and the passivation layer 133 may be exposed in a spacebetween adjacent metallic patterns MP.

As illustrated in FIG. 6B, each of the plurality of metallic patterns MPmay have a hexagonal shape in plan view, each of the plurality ofmetallic patterns MP may be disposed to be spaced apart from each other,and the passivation layer 133 may be exposed in a space between adjacentmetallic patterns MP.

As illustrated in FIG. 6C, each of the plurality of metallic patterns MPmay have a circular shape in plan view, each of the plurality ofmetallic patterns MP may be disposed to be spaced apart from each other,and the passivation layer 133 may be exposed in a space between adjacentmetallic patterns MP.

Shapes in plan view of the plurality of metallic patterns MP illustratedin FIGS. 6A to 6C are merely examples, and embodiments are not limitedthereto. The plurality of metallic patterns MP may have various othershapes in plan view.

FIGS. 7A to 7D are views schematically illustrating optical paths inaccordance with a distance between the plurality of metallic patterns inthe electroluminescent display device according to the embodiment of thepresent disclosure. Description will be given with reference to FIG. 4and FIGS. 7A to 7D.

In FIGS. 7A to 7D, it is shown that an angle θ formed between the secondsurface M2 and the first inclined surface M3 and an angle θ formedbetween the second surface M2 and the second inclined surface M4 of eachof the plurality of metallic patterns MP of the electroluminescentdisplay device 100 of FIG. 3 are equal, i.e., 30°, and optical paths inaccordance with changes in the distance G between the plurality ofmetallic patterns MP are illustrated.

FIG. 7A illustrates an optical path in a case in which the distance Gbetween the plurality of metallic patterns MP is 0.5 μm, FIG. 7Billustrates an optical path in a case in which the distance G betweenthe plurality of metallic patterns MP is 1 μm, FIG. 7C illustrates anoptical path in a case in which the distance G between the plurality ofmetallic patterns MP is 1.5 μm, and FIG. 7D illustrates an optical pathin a case in which the distance G between the plurality of metallicpatterns MP is 2 μm.

Comparing FIGS. 7A to 7D, it can be recognized that light extractionefficiency is the highest in the case shown in FIG. 7C in which thedistance G between the plurality of metallic patterns MP is 1.5 μm.

That is, in a non-micro cavity area NMCA, which is an area correspondingto the side surfaces P2 and P3 of the plurality of protruding portionsPP and the connecting portions CP of the reflective electrode RE that donot contact the first electrode 141, an amount of light, which has beenunable to be output to the outside due to being totally reflected insidethe light-emitting diode D, that is reflected upward through shapes ofthe connecting portions CP of the reflective electrode RE and extractedto the outside may be the greatest.

Also, by forming the micro cavity area and the non-micro cavity area tohave a ratio in a range of 1:1 to 5:1, and preferably, 1:1, thephenomenon in which luminance decreases and the color shift occurs inaccordance with a change in a viewing angle may be improved while lightextraction efficiency is improved.

Accordingly, in the electroluminescent display device 100 of FIG. 3according to the embodiment of the present disclosure, light extractionefficiency may be further improved when the distance G between theplurality of metallic patterns MP is 1.5 μm.

FIGS. 8A to 8C are views schematically illustrating optical paths inaccordance with an angle between a second surface and each of first andsecond inclined surfaces of each metallic pattern of anelectroluminescent display device according to the embodiment of thepresent disclosure. Description will be given with reference to FIG. 4and FIGS. 8A to 8D.

FIG. 8A illustrates an optical path in a case in which an angle θ formedbetween the second surface M2 and each of the first and second inclinedsurfaces M3 and M4 of each metallic pattern MP is 30°, FIG. 8Billustrates an optical path in a case in which an angle θ formed betweenthe second surface M2 and each of the first and second inclined surfacesM3 and M4 of each metallic pattern MP is 45°, and FIG. 8C illustrates anoptical path in a case in which an angle θ formed between the secondsurface M2 and each of the first and second inclined surfaces M3 and M4of each metallic pattern MP is 60°.

Comparing FIGS. 8A to 8C, it can be recognized that light extractionefficiency is high in the cases shown in FIGS. 8A and 8B in which theangle θ formed between the second surface M2 and each of the first andsecond inclined surfaces M3 and M4 of each metallic pattern MP is 30°and 45°. It can be recognized that light extraction efficiency issomewhat decreased when the angle θ formed between the second surface M2and each of the first and second inclined surfaces M3 and M4 of eachmetallic pattern MP is 60°.

That is, in the cases in which the angle θ formed between the secondsurface M2 and each of the first and second inclined surfaces M3 and M4of each metallic pattern MP is 30° and 45° in a non-micro cavity areaNMCA, which is an area corresponding to the side surfaces P2 and P3 ofthe plurality of protruding portions PP and the connecting portions CPof the reflective electrode RE that do not contact the first electrode141, an amount of light, which has been unable to be output to theoutside due to being totally reflected inside the light-emitting diodeD, that is reflected upward and extracted to the outside may be thegreatest.

Therefore, in the electroluminescent display device 100 of FIG. 3according to the embodiment of the present disclosure, light extractionefficiency may be further improved when the angle θ between the secondsurface M2 and each of the first and second inclined surfaces M3 and M4of each of the plurality of metallic patterns MP is formed to be in arange of 30° to 45°.

As described above, in the electroluminescent display device 100 of FIG.3 according to the embodiment of the present disclosure, lightextraction efficiency and color reproduction rate may be improved usingthe micro cavity phenomenon in the micro cavity area MCA in which thefirst electrode 141 contacts the top surfaces P1 of the plurality ofprotruding portions PP of the reflective electrode RE.

Further, in the non-micro cavity area NMCA corresponding to the sidesurfaces P2 and P3 of the plurality of protruding portions PP and theconnecting portions CP of the reflective electrode RE that do notcontact the first electrode 141, a viewing angle may be widened due tomixing of the light L1 of FIG. 5 output from the micro-cavity area MCAand the light L2 of FIG. 5 output from the non-micro cavity area, whilelight extraction efficiency is further improved due to upward reflectionof light, which has been unable to be output to the outside due to beingtotally reflected inside the light-emitting diode D, so that the lightmay be extracted to the outside.

That is, since the straightness of light output is decreased due to theshape of the reflective electrode RE and light is output in a lateraldirection in the non-micro cavity area NMCA, the phenomenon, in whichluminance decreases and a color shift occurs from a color with a longwavelength to a color with a short wavelength due to an increase in aviewing angle, which occurs in the related art electroluminescentdisplay device to which the micro cavity effect is applied, may beeffectively prevented.

Particularly, by forming the distance G between the plurality ofmetallic patterns MP to be 1.5 μm and forming the angle θ formed betweenthe second surface M2 and each of the first and second inclined surfacesM3 and M4 of each of the plurality of metallic patterns MP to be in arange of 30° to 45°, the phenomenon in which luminance decreases and acolor shift occurs due to an increase in a viewing angle may be moreeffectively prevented.

In the present disclosure, by disposing a plurality of metallic patternsto be spaced apart from each other under a light-emitting diode andforming a reflective electrode configured to cover the plurality ofmetallic patterns, a viewing angle can be widened while light extractionefficiency is improved.

The present disclosure has been described above with reference toexemplary embodiments thereof. However, those of ordinary skill in theart should understand that various modifications and changes may be madeto the present disclosure within the scope not departing from thetechnical spirit and scope of the present disclosure described in theclaims below.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet, including butnot limited to [insert list], are incorporated herein by reference, intheir entirety. Aspects of the embodiments can be modified, if necessaryto employ concepts of the various patents, applications and publicationsto provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. An electroluminescent display device, comprising: a thin filmtransistor disposed on a substrate; a passivation layer disposed on thethin film transistor; a plurality of metallic patterns disposed spacedapart from each other on the passivation layer; a reflective electrodedisposed conforming to the shape of the plurality of metallic patternsand also to a top surface of the passivation layer and including aplurality of protruding portions; an overcoat layer disposed on thepassivation layer and the reflective electrode and including an openingthat exposes a top surface of each of the plurality of protrudingportions; a first electrode disposed on the reflective electrode and theovercoat layer and electrically connected to the reflective electrode;an light-emitting layer disposed on the first electrode; and a secondelectrode disposed on the light-emitting layer.
 2. Theelectroluminescent display device of claim 1, wherein each of theplurality of metallic patterns includes a first surface contacting a topsurface of each of the plurality of protruding portions, a secondsurface contacting the passivation layer and having an area greater thanthat of the first surface, and first and second inclined surfacesconnecting the first surface and the second surface.
 3. Theelectroluminescent display device of claim 1, wherein a distance betweenadjacent two of the plurality of metallic patterns is in a range of 0.5μm to 2 μm.
 4. The electroluminescent display device of claim 1, whereina height of the plurality of metallic patterns is in a range of 0.5 μmto 1 μm.
 5. The electroluminescent display device of claim 2, wherein alength of the first surface is in a range of 1 μm to 5 μm.
 6. Theelectroluminescent display device of claim 2, wherein an angle formedbetween the second surface and each of the first and second inclinedsurfaces is in a range of 20° to 70°.
 7. The electroluminescent displaydevice of claim 2, wherein the first electrode, the light-emittinglayer, and the second electrode are disposed to be flat in an emissivearea.
 8. The electroluminescent display device of claim 1, wherein thereflective electrode is electrically connected to the thin filmtransistor.
 9. The electroluminescent display device of claim 1, whereinthe first electrode is electrically connected to the thin filmtransistor.
 10. An electroluminescent display device, comprising: asubstrate including one or more pixels; and a light-emitting structuredisposed in each of the pixels, wherein the light-emitting structurecomprises a second electrode, a reflective electrode, and alight-emitting layer disposed between the second electrode and thereflective electrode, or comprises a second electrode, a reflectiveelectrode, a light-emitting layer disposed between the second electrodeand the reflective electrode, and a first electrode disposed between thelight-emitting layer and the reflective electrode, wherein each of thepixels comprises a plurality of micro cavity areas disposed to be spacedapart from each other and one or more non-micro cavity area disposedbetween the micro cavity area, a combined thickness in a verticaldirection of the light-emitting structure from the reflective electrodeto the second electrode has a different value in the micro cavity areafrom that in the non-micro cavity area, and the light-emitting structureis configured to produce a micro cavity effect, and wherein each of thesecond electrode and the reflective electrode is formed to be flat inthe micro cavity area and at least one of the second electrode and thereflective electrode is formed to comprise a non-flat surface in thenon-micro cavity area or wherein each of the first electrode, the secondelectrode, and the reflective electrode is formed to be flat in themicro cavity area and at least one of the first electrode, the secondelectrode, and the reflective electrode is formed to comprise a non-flatsurface in the non-micro cavity area.
 11. The electroluminescent displaydevice of claim 10, wherein the combined thickness in a verticaldirection of the light-emitting structure from the reflective electrodeto the second electrode has a smaller value in the micro cavity areathan that in the non-micro cavity area.
 12. The electroluminescentdisplay device of claim 10, wherein each of the plurality of microcavity areas is formed to have a circular, rectangular, square, diamond,hexagonal or other polygonal shape disposed to be spaced apart from eachother in one or each pixel.
 13. The electroluminescent display device ofclaim 10, wherein the reflective electrode includes an inclined surfacetowards the light-emitting layer in the non-micro cavity area.
 14. Theelectroluminescent display device of claim 10, wherein each of theplurality of micro cavity areas has a length in a lateral direction ofthe substrate in a range of 1 μm to 5 μm.
 15. The electroluminescentdisplay device of claim 13, wherein the reflective electrode comprises,towards the light-emitting layer, at least two inclined surfaces and oneflat surface parallel to the light-emitting layer in the micro cavityarea.
 16. The electroluminescent display device of claim 15, wherein theflat surface of the reflective electrode in the micro cavity area has alength in a range of 1 μm to 5 μm,
 17. The electroluminescent displaydevice of claim 15, wherein an angle formed between the inclined surfaceand a lateral direction of the substrate is in a range of 20° to 70°.18. The electroluminescent display device of claim 10, furthercomprising: a passivation layer disposed on a side of the reflectiveelectrode opposite to the first electrode; a plurality of metallicpatterns disposed to be spaced apart from each other between thereflective electrode and the passivation layer; and an overcoat layerdisposed between the first electrode and the reflective electrode. 19.The electroluminescent display device of claim 18, wherein each of theplurality of metallic patterns includes a first surface in the microcavity area contacting a top surface section of the reflectiveelectrode, a second surface contacting the passivation layer and havingan area greater than that of the first surface, and first and secondinclined surfaces connecting the first surface and the second surface.20. The electroluminescent display device of claim 18, wherein adistance between adjacent two of the plurality of metallic patterns isin a range of 0.5 μm to 2 μm.
 21. The electroluminescent display deviceof claim 18, wherein a height of the plurality of metallic patterns isin a range of 0.5 μm to 1 μm.
 22. The electroluminescent display deviceof claim 19, wherein a length of the first surface is in a range of 1 μmto 5 μm.
 23. The electroluminescent display device of claim 19, whereinan angle formed between the second surface and each of the first andsecond inclined surfaces is in a range of 20° to 70°.